Type I diabetes (T1D) is a common and devastating disease characterized by autoimmune destruction of the insulin-producing beta cells of the pancreas. The ensuing condition leaves the affected patients unable to produce sufficient insulin for proper metabolic and glycemic control, resulting in acute and chronic complications that cause extensive morbidity and mortality. There is considerable hope, however, that T1D may be preventable, or even reversed, with the timely administration of immunosuppressive therapy. No such therapy has yet been approved, and considerable need exists for the development of novel T1D therapeutics. Interleukin-2 (IL-2) is an immunoregulatory cytokine with critical importance to the etiology of T1D: while IL-2 is essential to maintain the regulatory T cells (Tregs) that prevent the disease, it also stimulates autoreactive lymphocytes that attack the pancreas and cause T1D. This proposal describes the engineering of novel IL-2 based therapeutics tailored for the prevention and treatment of T1D by splitting the antithetical functions of IL-2 that occur in T1D. IL-2 analogues will be designed through rationale, site-directed mutagenesis (Aim 1) and through a combinatorial approach that couples yeast-surface display to phosphoflow cytometry to screen thousands of IL-2 variants on the basis of signaling output (Aim 2). Functional characterization of these synthetic IL-2 molecules will include in vitro asays of IL-2 dependent cellular functions, such as T cell proliferation and NK cell cytotoxicity. Biophysical characterization of these IL-2 analogues will employ surface plasmon resonance to measure affinities and binding kinetics to the IL-2 receptor subunits and x-ray crystallography to determine the molecular structures of the IL-2/IL-2 receptor complexes. Ultimately, and most importantly, candidate IL-2 therapeutics developed through the methods above will be assessed for efficacy in the prevention and treatment of diabetes in the non-obese diabetic (NOD) mouse model of T1D. Thus, through these multidisciplinary and translational studies, we will advance new candidate T1D therapies for clinical development. !